This section introduces aspects that may help to facilitate a better understanding of the invention(s). Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
Currently, when two user equipments (UEs) in close proximity communicate with each other, their data path goes via the operator network. The typical data path for this type of communication may be referred to as infrastructure cellular mode, where enhanced Node B (eNB) and/or gateway(s) (GW(s)) are involved.
In addition, Device-to-Device (D2D) communications are discussed extensively as candidate for essential enablers for future wireless communication systems-5G (the 5th generation). If UEs are in proximity of each other, they may be able to use a local or direct path.
FIG. 1 shows a proximity communication scenario where two UEs communicate using a locally-routed (optimized) path via eNB, which may be referred to as locally-routed mode. As shown in FIG. 1, two UEs (UE1, UE2) and two eNBs (eNB1, eNB2) are shown for illustration. The two UEs communicate via the eNB1 and they are both served by the same eNB and exchange control information with the eNB (or other nodes of the network).
FIG. 2 shows another proximity communication scenario where two UEs communicate using a direct path, which may be referred to as direct mode. As shown in FIG. 2, two UEs (UE1, UE2) and two eNBs (eNB1, eNB2) are shown for illustration. The two UEs communicate via a direct path therebetween.
D2D communication provides low power and high data rate communications between end-users. Also due to the local process at device itself or eNB (for optimized path), the communication latency can be really short. However, it is not always possible to provide low latency reliable communication between users due to mobility. For instance, if due to mobility, one UE of the D2D pair needs to handover to another eNB, due to the possible non-ideal backhaul connection between eNBs, it is not easy to keep the ongoing delay-sensitive applications.
In WO2011/109027A1, methods for D2D handovers are provided. The methods hand over both D2D devices rather than maintaining a multi-cell D2D configuration in which each D2D device is coupled to a separate base station.